Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: Reduce ejection port noise, suppressed 9mm ar

  1. #1
    Join Date
    Oct 2011
    Location
    Utah
    Posts
    2,764
    Feedback Score
    0

    Reduce ejection port noise, suppressed 9mm ar

    I would like to hear recommendations to reduce the ejection port noise on my suppressed 9mm sbr.

    Specs:
    Qc10 colt pattern lower
    Vltor mur upper
    Jp bolt
    9mm silent captured spring buffer system (off the shelf, std weights and springs)
    Qc10 3.5 inch barrel
    Silencerco Octane 45
    Primary ammunition is Winchester train and defend 147g (train variety)

    The weapon is reasonably quiet, but exhibits significant ejection port bark
    Function is 100% reliable, 0 malfunctions to date.

    I would like to quiet it down more, but obviously not at the expense of reliability. Not sure how much is possible with blowback operation.

    I assume my only real option is increasing the buffer weight, but I am open to all options and suggestions.
    Go Ukraine! Piss on the Russian dead.

  2. #2
    Join Date
    Oct 2015
    Posts
    501
    Feedback Score
    0
    Adjustable gas block.

    From what iv read, micromoa govnah vs slr rifleworks adj block

    Sent from my SM-G900P using Tapatalk

  3. #3
    Join Date
    Jan 2012
    Posts
    965
    Feedback Score
    24 (100%)
    Quote Originally Posted by daniel87 View Post
    Adjustable gas block.

    From what iv read, micromoa govnah vs slr rifleworks adj block

    Sent from my SM-G900P using Tapatalk
    9mm don't have gas blocks


    Sent from my Z797C using Tapatalk

  4. #4
    Join Date
    Nov 2010
    Location
    MI
    Posts
    3,516
    Feedback Score
    22 (100%)
    Pretty much the only option with a blowback gun is to increase the reciprocating mass.


    The JP 9mm spring thing looks to be around 4.5 oz, while the BCG is lighter than a normal 9mm BCG because the tail is hollow.

    Many 9mm carbines can run with a normal 9mm BCG (~14+oz) and ~5.4 oz 9mm buffer, unsuppressed.

    There are also 17 oz carriers and 8.5 oz buffers commercially available.


    It seems the reciprocating mass is too low, resulting in high bolt speed and ejection port bark.
    Black River Tactical
    BRT OPTIMUM Hammer Forged Chrome Lined Barrels - 11.5", 12.5", 14.5", 16"
    BRT EZTUNE Preset Gas Tubes - PISTOL, CAR, MID, RIFLE
    BRT Bolt Carrier Groups M4A1, M16 CHROME
    BRT Covert Comps 5.56, 6X, 7.62

  5. #5
    Join Date
    Oct 2011
    Location
    Utah
    Posts
    2,764
    Feedback Score
    0
    Yeah, that is where my head is already. I bought this as a used pistol build with a 7 inch barrel. I doubt I would have gone scs, but since it has been so reliable I have been hesitant to change it. (ie: fix it till it's broke) Just thought I would post the question before I ordered a heavy buffer. I am thinking of going to the 12.5 oz adjustable and working down if necessary.

    As a last resort, I suppose I could install the adjustable gas block on my unported barrel just so I could say I tried everything
    Last edited by utahjeepr; 12-31-16 at 16:19.
    Go Ukraine! Piss on the Russian dead.

  6. #6
    Join Date
    Jan 2013
    Posts
    2,688
    Feedback Score
    40 (100%)
    If it was not a JP system I would say you need a heavier buffer - spikes ST-9X or the 9mm-Q Buffer from http://heavybuffers.com/. Makes all the difference in the world.

    With the JP system I would give them a call and tell them what you are trying to do and they may have a solution for you.

  7. #7
    Join Date
    Nov 2010
    Location
    MI
    Posts
    3,516
    Feedback Score
    22 (100%)
    You probably want a total mass around 22.5 oz for normal operation and a bit more for the suppressor use.

    Another option that may work well is to put an VLTOR A5H4 buffer ( 7 oz ) and spring in the carbine tube.

    Depending on the carrier, the A5H4 may not bring the total up enough.

    The 9mm QT will certainly do it.
    Black River Tactical
    BRT OPTIMUM Hammer Forged Chrome Lined Barrels - 11.5", 12.5", 14.5", 16"
    BRT EZTUNE Preset Gas Tubes - PISTOL, CAR, MID, RIFLE
    BRT Bolt Carrier Groups M4A1, M16 CHROME
    BRT Covert Comps 5.56, 6X, 7.62

  8. #8
    Join Date
    Oct 2011
    Location
    Utah
    Posts
    2,764
    Feedback Score
    0
    So as I do more research (aka over thinking) I have found a greater number of options.

    1) Add more mass to the scs. I can replace the only steel weight with tungsten this should get me to around 5.2/5.3 oz. Probably not enough to be effective.

    2) I can use an A5 7 oz of heavy buffers A5 10 oz in the carbine extension with a rifle spring. Bad idea in a 5.56 but works to limit the overtravel in a 9mm. Adds mass, but I don't believe it would add the benefits normally attributed to the A5 system in a 5.56 gun.

    3) use a 9mm heavy buffer up to 12.5 oz with a carbine spring. Adds the most mass. I don't see any functional difference between this and option 2 other than that.

    4) use a 9mm heavy buffer up to 12.5 oz with a sprinco orange .308 carbine spring. Adds mass equal to option 3 but the heavier rate spring may control the higher recip mass better.

    5) it may be possible to run the 7 or 10 oz buffer and rifle spring in an A5 extension and gain the smoother impulse of the A5 (not really sure how much it would help a 9mm) without having overtravel and broken bolt catch issues. Not likely to try this but it is an option.

    See any obvious winners? Or am I really just over thinking this?

    ETA: I realize I could also switch to a heavier carrier, but since the carrier and the buffer effectively act as a unit I don't see an advantage to adding mass to one vs the other so long as the recip mass is increased.
    Last edited by utahjeepr; 01-01-17 at 08:30.
    Go Ukraine! Piss on the Russian dead.

  9. #9
    Join Date
    Jan 2013
    Posts
    2,688
    Feedback Score
    40 (100%)
    The crutch of the issue in my mind is the JP system. I am not bashing it but it is its own animal. I have worked with the JP on blackout questions in the past and they have been super knowledgeable. They may have a cheap solution that works with the silent captured spring be it weights or springs that will slow down the system.

  10. #10
    Join Date
    Oct 2011
    Location
    Utah
    Posts
    2,764
    Feedback Score
    0
    I definitely agree that the scs is its own animal. While I would probably have never purchased the scs on my own, it came with the pistol when I bought it. Unsuppressed it works great, and has been completely reliable. In a gas gun even suppressed I can see how it would have it's proponents. Unfortunately for my wallet I believe it is simply out of it's element in suppressed blowback operation. While the weapon is certainly still functional the bark is undesirable. The scs is very close to maxed out in terms of mass in 9mm configuration. I can switch one steel weight to tungsten. Unless I am mistaken in the operating principles, the springs only have a small amount of control over the travel of the recip mass and have virtually no effect on the initial travel (opening of the port) of the bolt.

    While I am certainly willng/interested in seeing what JP may have to say, I don't expect any game changing information. The one possibility I see is in the weights for the maxim stock scs. It appears they are able to use fewer weights on that shorter system leading me to belive that those are heavier. If they are, and lf they can be used with a standard 9mm scs without causing issues that might open up another set of options.

    I have however been considering replacing the scs for completely different reasons. Namely that at least with the trigger I have (SSA-E) the reciever extension has to be removed in order to remove the scs for cleaning/lube. While this is not a terrible drawback, I would much prefer to have the R.E. castle nut staked and leave it alone, especially now that it is an SBR.

    I am looking forward to learning more from JP after the holiday even if does not address my application. I am certainly glsd to hear that they are good folks to talk to/ learn from and that they were able to help you tune your 300 gas gun.
    Go Ukraine! Piss on the Russian dead.

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •